Solid-phase microextraction (“SPME”) is a method of chemical sample preparation and introduction. SPME is typically used for extraction, preconcentration, and introduction of trace level analytes from very dilute solutions into chromatographic separation systems. One advantage of the SPME method is that SME requires no solvent for extraction; the mechanism for extraction and preconcentration is based on physical phenomenon such as adsorption and absorption of analyte by sorbents supported by solid materials such as porous glass fibers. SPME methodology is highly useful for rapid quantitative testing of dilute organic pollutants with the use of little or no hazardous solvents that are used in other similar analytical methods, such as high performance liquid chromatography. Extraction and preconcentration of analytes with SPME can be potentially based on any of a variety of physical mechanisms, including adsorption and absorption, making SPME a versatile analytic tool.
SPME uses a “sorbent” or “adsorbent” material such as carbowax (“CAR”), polydimethylsiloxane (“PDMS”), Carboxan, and divinylbenzene (“DVB”), that can potentially adsorb or absorb a target analyte (the “sorbent” or “adsorbent”) from its environment. As noted above, the sorbent is typically supported by a fiber tip (the “tip”) that is adhered to a metal base via an adhesive epoxy substance. To extract and preconcentrate a target analyte, the coated tip can be used in either of two ways depending on the volatility of the target analytes. The coated tip is either (1) placed in the headspace of a vial containing the solution of volatile analytes, or (2) dipped into the solution directly in the case of non-volatile analytes. Several comprehensive review articles exist which detail the various methodologies and applications involving SPME technology. See, Hook, et al., Solid-phase microextraction (SPME) for rapid field sampling and analysis by gas chromatography-mass spectrometry (GC-MS); Trends Anal. Chem. 21: 534-543 (2002); Snow et al.; Head-space analysis in modern gas chromatography; Trends Anal. Chem. 21: 608-617 (2002); Theodoridis et al., Solid-phase microextraction for the analysis of biological samples. J. Chromatogr. B. 745: 49-82 (2000); each of which is incorporated by reference herein.
Presently available SPME tips are constructed by impregnating or coating the concentrating material (the “adsorbent”) onto a porous silica fiber tip as discussed in U.S. Pat. No. 5,691,206 to Pawliszyn (the “Pawliszyn patent”). The fiber tip is constructed of fused silica fibers similar to those referred to as “optic fibers,” with the tip being chemically treated to increase its porosity. The fiber tip is then attached with an adhesive substance (such as an epoxy) or crimped to a metal rod. A sorbent material (which is the active preconcentration agent) is coated onto the fiber.
The glued or crimped junction between the metal rod and the fiber tip is problematic in these devices; it is easily weakened and the coated fiber can break free from the supporting metal rod quite easily. While the chemically treated fiber tip disclosed in the Pawliszyn patent has proven to adhere well to a wide range of adsorbents, the Pawliszyn patent admits that such treated fibers are fragile and require a metal housing (sometimes referred to as a needle) to protect the fiber. Col. 4, lns. 10-20. Further, later changes to improve the rod/fiber interface by crimping the fiber onto a flexible metal support provides better stability, but the tip is still prone to breakage, particularly when working with a solvent that has the ability to swell the coating or dissolve the adhesive.
Therefore, a more rugged SPME tip for supporting the adsorbent without significantly reducing sensitivity of the SPME method would be appreciated. In addition, an SPME tip that eliminates analysis downtime, reduces cost, and facilitates analysis in difficult environments unable to be tested by the prior devices would be appreciated by those in the art.